1. Field of the Invention
This invention relates to a simulator for providing a visual display, particularly to a night-time or dusk scene. The invention has particular utility in the context of aircraft training simulators, but it could be used for other purposes.
In the training of a pilot to land an aircraft at night on an airfield by the use of a simulator, it is important to provide a display of the airfield lights situated in their correct positions. The more realistic the display can be made, the better is the training provided by the simulator. For this purpose it is desired to display the effects of buildings and hills and to provide a "horizon glow".
In real life, of course, some of these features can obscure others, depending on the precise viewpoing of the observer at any instant, and for example where a building stands in front of a light, it is undesirable for the display to show the light apparently shining through the solid building.
It is desirable, therefore, to eliminate the light from the display, i.e., to occult it.
2. The Prior Art
In an aircraft simulator, such a display is provided by a cathode ray tube (CRT) visual display unit (VDU) which is controlled by a computer. The data base containing all the positional data of the features to be displayed customarily is stored in a general purpose computer, which also selects the required data to be displayed in any given scene. A perspective transformation then is carried out on the data in a specially arranged unit. Finally, another specially arranged unit provides image generation from the transformed data. Such equipment is known already.
One arrangement suggested is to use the general purpose computer to calculate whether or not any given string of lights is behind an object, when it is, and to prevent its transfer to the perspective transformation unit. This is believed to be unrealistic because only complete strings of lights and surfaces can be eliminated from the scene. Further, the software necessary to perform the perspective view in the scene is very complex, and therefore, a very powerful computer is required.
In another arrangement, the display provides a raster display; that is, the scene is built up by scanning lines in the manner that a television picture is developed. Each raster is added to a large memory in the image generation system. Such memory, therefore, provides a memory location for every element of the display. Subsequent features are checked against this memory for coincidence with a previously memorized area.
This last-described arrangement overcomes some of the problems that have been experienced and is effective for surfaces, e.g., buildings, providing certain range ordering rules are adhered to. However, it is necessary for all light points to lie behind all the occulting surfaces, so that only one level of occulting exists for light points. Even so, the size of the memory required is very large, e.g., for one thousand line resolution, one million bits of storage would be needed.
Another disadvantage of this last-described arrangement is that it is based on a raster scan, which does not provide the best form of display. It is desirable to provide surfaces with a texture, and this is best achieved using a calligraphic display, in which surface areas are built up by close lines which are oriented in whatever is the best orientation for that surface. For example, for buildings and horizon glow, this may be vertical, while for the runway, the lines may converge at a distant point.